A known process for the exchange of data between telecommunications and data processing systems, in the case where the telecommunications system provides "incoming service only" for the data processing system, takes place e.g. via the internationally standardized S2-interface with 2 MBit/s (PABX-Host-Coupling; "Computer Integrated Telephony (CIT)" (Computer inside the telephone line), Radio Show 16/1990, p. 55-58).
Another known process consists of converting data processors into "extra-feature-telephones" by means of corresponding software, so that both devices are combined in one data processor, for example a personal computer. In the event a second signalling channel is open, a so-called ISDN-B-Channel, a data link to another corresponding data processor is established, simultaneously with the voice service, which provides rapid transfer of data (ISDN-Terminals Experience Report; "The PC As An Extra-Feature-Telephone And More" Radio Show 26/1989, p. 31-34).